The father of a mentally ill Ontario man who died at the hands of police said he's disappointed that an inquest jury found the use of a Taser only contributed to — rather than caused — his son's death, saying Tuesday's decision shows how little is known about the potentially lethal effects of stun guns.

That the jury clearly linked Aron Firman's death in June 2010 to the shock he received nonetheless brought some small satisfaction to his father, Marcus Firman, following weeks of often contradictory evidence from experts.

"Obviously the science is unclear," he said after the ruling came in what Ontario's top pathologist has called an "index case."

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"Officers should be aware of the results of using a Taser, or the potential results of using a Taser. They may be rare circumstances but they do... happen, as was shown," he said.

At the crux of the case was how much of a role a stun gun played in the 27-year-old's death.

Firman, a man with schizophrenia, died after an encounter with Ontario Provincial Police in Collingwood, Ont. Ontario's police watchdog cleared the officers of any wrongdoing, but said the Taser's deployment caused Firman's death.

In its verdict Tuesday, the five-member jury panel deemed the use of a Taser to be "a contributing factor."

It ruled the cause of death was cardiac arrhythmia due to a state of excited delirium — a condition sometimes cited as a cause of death in people using cocaine or those with severe mental illness — and schizophrenia.

A lawyer for Taser International has suggested that was the cause during the inquest. He was not present for the verdict.

Firman's father, however, said he remains convinced the stun gun triggered the heart condition that proved fatal for his son.

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The panel also found Firman's death was "accidental," as his family had suggested, rather than "undetermined," as Taser International had argued.

Presiding coroner William Lucas warned the five-member jury panel on Friday not to resort to an "undetermined" cause of death as a matter of convenience.

The inquest, which sat intermittently since April, heard vastly different testimony from experts. Some suggested the use of a Taser on Firman was a key factor in his death, while others argued the stun gun had little to do with the fatality.

The case proves there is a need for thorough research on Tasers and how to minimize the risks associated with their use, said the family's lawyer Sunil Mathai.

Measures to collect data on police use of stun guns were among the panel's recommendations aimed at preventing such deaths in the future.

Others included further training for officers on dealing with mentally ill people, and instructions for police officers to call paramedics and begin CPR immediately when someone becomes unresponsive after being struck with a Taser.

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Current procedures require that officers first check for a pulse.

Aron Firman was a resident at a group home in Collingwood, Ont., at the time of his death.

A December 2010 report from Ontario's Special Investigations Unit said that on June 24 of that year two OPP officers responded to an assault complaint about Firman and found him sitting in a chair outdoors.

Both officers attempted to speak to "an agitated" Firman, according to the report. When they moved to apprehend him Firman got out of his chair and "moved aggressively" towards an officer, it said.

The second officer tried to intervene but was unable to do so as Firman hit her in the face with his elbow, said the report. Firman then moved toward the first officer who responded by discharging his Taser gun at him.

Firman was able to take a few additional steps before falling to the ground and losing consciousness, the report said. He was taken to an area hospital where he was pronounced dead.

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His father has described him as a gentle, artistic and inquisitive man who was keenly aware of his "terrible illness." Both parents have said their son's loss had left an aching void in their lives.

Relatives embraced and comforted each other Tuesday at the end of what Marcus Firman described as a long and arduous inquest.

Still, nothing can ease the pain of his son's death, he said.

"I will always miss my son. The grief is so, so much that you don't forget, you cannot forget. He's a part of me and I'm sure the rest of the family feels the same way.

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